1. Field of Invention
The present invention relates to a system for acquiring and recording signals delivered by a set of sensors disposed in one or more probes lowered into a well.
2. Description of the Prior Art
The acquisition of measurement data in a borehole is generally achieved by lowering therein one or more probes suspended from a multi-function cable. The probe comprises an elongated body and one or more mobile arms. Hydraulic jacks cause each arm to move from a rest position against the body of the probe to an opened out position where they anchor themselves against the wall of the borehole and thus immobilize the probe. Hydraulic circuits connect the jacks to means for delivering pressurized fluid generally comprising an electric motor and solenoid valves. The multi-function cable very often comprises a plurality of conducting lines for transmitting electric currents feeding the motor and signals of all kinds. They may for example be control signals transmitted to the probe from a surface installation and response signals sent back from the probe. The response signals are formed either by check or test signals or data measured by the sensors of the probe. Such a probe is described for example in French Pat. No. 2.501.380 or the U.S. Pat. No. 4,428,422.
It is also possible for example to use a probe having anchorage arms actuated by springs which are held tensioned by bolts during lowering Hydraulic means comprising solenoid valves actuated by control signals received through the multi-function cable. Such a probe is described for example in French Pat. No. 2,548,727 or the corresponding U.S. Pat. No. 4,616,703.
The different sensors lowered into the well for making measurements of different kinds may be included in a single probe or else in a set of probes comprising a main probe under which a plurality of satellite probes are suspended at different depths. Such a probe assembly is described for example in French Pat. No. 2.564.599.
Seismic prospection operations are carried out for example by disposing in wells a plurality of sensors adapted for detecting waves reflected back by the discontinuities of the subsoil, coming from a seismic source disposed on the surface or in the vicinity thereof, or else in another well. The signals received are used so as to obtain seismic sections of the subsoil. The seismic sensors are generally directional and oriented in one or more directions orthogonal to each other. They are disposed in an assembly of cell probes so as to pick up the seismic signals received at different depths levels and are connected to a surface recording station either directly by means of a special line included in the multi-function cable or through a seismic acquisition apparatus. In this case, the different signals are connected, sampled, digitized and transmitted over one or more lines of the multi-function cable in coded form. After decoding, they are recorded and processed by a laboratory.
The number of different sensors in a seismic reception device may vary particularly depending on the configuration of the reception assembly used.
In some cases, a single well probe is used having a compartment for one or two three-dimensional sensors comprising for example, three sensitive directional elements whose axes are oriented in three directions orthogonal to each other. In other cases, an assembly of several probes is lowered into the borehole, suspended below each other and each containing at least one sensor. An acquisition apparatus is disposed in the main probe. It is connected to the sensors housed in the different probes. It may be a question of directional sensors or else of three-dimensional sensors. The number of seismic channels to be acquired is therefore very variable and it is important that the acquisition apparatus used may be readily adapted to very different sensor configurations.